There is much good in what you write, but I think you have a false dichotomy: do what you love vs. do what you can. Except for the most infantile aspirants one learns what they love by doing or trying to do. Your advice would suggest taking whatever comes your way, rather than aspiring to something new, bigger, or broader. Finding what one loves is an exploration.
It may be a false dichotomy in another direction. E.g. I might want to write, but not novels. Or maybe writing is part of the thing I want to do and I love that writing, but it stories or articles on the biology of tree roots.
Most people are not professional writers in any of it’s many possible manifestations, but they are often parts of a creative process (business, science, engineering, movies, art, etc.) in which there are many different roles. Most will seek their fulfillment within these projects. I don’t think you intend to discourage exploration within these constraints.
Perhaps you sense that many people are suffering because they aspire to something they can never achieve and seek to alleviate that suffering. I think we would be better advised to encourage exploration rather than attachment to some dream profession. If someone says they want to write a book, encourage them to explore. Advise them on the difficulties and moderation and the grace to fail, learn, and move on.